Merge pull request #34 from code-dot-org/feature/dim_student_status

built dim_student_status first draft

dbt/models/marts/students/dim_student_status.sql

@@ -0,0 +1,132 @@
+/*
+
+Design: 1 row per student, school_year, churn_status
+Logic: we can determine status based on three properties we can compute for every user|school_year as a binary:
+    - 0/1 they are active this school_year - (A)ctive
+    - 0/1 they were active in the previous school_year - (P)rev year
+    - 0/1 they have ever been active in ANY school_year prior, incl. prev year - (E)ver before
+
+    Rather than write out long complicated combinational logic in code, these 3 values can be combined 
+    into an ordered 3-char string representing the concatenated true/false combinations for Active|Prev|Ever 
+    e.g. "101" means: ( Active = true AND Prev year = false AND Ever before = true )
+    To practice some defensive programming, we'll handle all cases exhaustively and return a 
+    sentinal '<impossible status>' value as a fast-fail value for cases that we believe to be impossible.
+
+    - '000' (0) = 'market'              -- Not active now + never been active
+    - '001' (1) = 'inactive churn'      -- NOT active + NOT active prev year + active ever before
+    - '010' (2) = '<impossible status>' -- should not be possible, active in the prev year should imply active ever before
+    - '011' (3) = 'inactive this year'  -- NOT active + active prev year + (active ever before implied)
+    - '100' (4) = 'active new'          -- active this year + NOT active last year + NOT active ever before
+    - '101' (5) = 'active reacquired'   -- Active this year + NOT active last year + active in the past
+    - '110' (6) = '<impossible status>' -- impossible for same reason as status (2)
+    - '111' (7) = 'active retained'     -- active this year + active last year + (active ever before implied)
+
+*/
+
+with 
+
+student_courses_started as (
+
+    select
+        student_id,
+        school_year,
+        listagg(distinct course_name, ', ') within group (order by course_name ASC) courses_started
+    from {{ ref('dim_student_courses') }}
+    group by 1, 2
+
+),
+
+all_student_users as (
+
+    select
+        student_id,
+        created_at
+    from {{ref('dim_students')}}
+
+), 
+
+school_years as (
+
+    select * from {{ref('int_school_years')}}
+
+), 
+
+all_students_school_years as (
+
+    select
+        u.student_id,
+        sy.school_year
+    from all_student_users u
+    join school_years sy on u.created_at <= sy.ended_at
+    where sy.started_at < current_timestamp
+
+), 
+
+active_status_simple as (
+
+    select
+        all_sy.student_id,
+        all_sy.school_year,
+        case when s.student_id is null then 0 else 1 end as is_active,
+        s.courses_started
+
+    from all_students_school_years all_sy
+    left join student_courses_started s on s.student_id = all_sy.student_id and s.school_year = all_sy.school_year
+
+), 
+
+full_status as (
+    -- Determine the active status for each student in each year
+
+    select
+        student_id,
+        school_year,
+        is_active,
+        courses_started,
+        coalesce(
+            lag(is_active, 1) 
+                over (partition by student_id order by school_year) 
+            , 0
+        ) as prev_year_active,
+        coalesce( --force any NULL to be 0 for this function
+            max(is_active) 
+                over (partition by student_id order by school_year rows between unbounded preceding and 1 preceding)
+            , 0
+        ) as ever_active_before,
+        (is_active || prev_year_active || ever_active_before) status_code
+    from
+        active_status_simple
+
+), 
+
+current_school_year as (
+
+    select 
+        school_year
+    from {{ref("int_school_years")}}
+    where current_date between started_at and ended_at
+
+)
+
+select
+    student_id,
+    school_year,
+    --is_active,
+    --prev_year_active,
+    --ever_active_before,
+    --status_code,
+    case 
+        when status_code = '000' then 'market'
+        when status_code = '001' then 'inactive churn'
+        when status_code = '010' then '<impossible status>'
+        when status_code = '011' then 'inactive this year'
+        when status_code = '100' then 'active new'
+        when status_code = '101' then 'active reacquired'
+        when status_code = '110' then '<impossible status>'
+        when status_code = '111' then 'active retained'
+    end as status,
+    courses_started
+from
+    full_status
+order by
+    student_id, school_year

dbt/models/marts/students/dim_students.sql

@@ -19,13 +19,19 @@ user_geos as (
     where user_id in (select student_id from students)
 ),
 
+school_years as (
+    select * from {{ref('int_school_years')}}
+),
+
 final as (
 select 
     students.*, 
-    user_geos.is_international
+    user_geos.is_international,
+    sy.school_year created_at_school_year
 from students 
 join user_geos 
     on students.student_id = user_geos.user_id
+left join school_years sy on students.created_at between sy.started_at and sy.ended_at
 )
 
 select *